const PENDING = "pending"; //等待
const FULFILLED = "fulfilled"; //成功
const REJECTED = "rejected"; //失败

class MyPromise {
    constructor(executor) {
        try {
            executor(this.resolve, this.reject);
        } catch (e) {
            this.reject(e)
        }
    }
    //promise 状态
    status = PENDING;
    value = undefined; //保存成功之后的值
    reason = undefined; //失败后的原因
    successCallback = []; //成功回调
    failCallback = []; //失败回调
    resolve = (value) => {
        //如果状态不是等待，阻止程序向下执行
        if (this.status !== PENDING) return;
        //将状态更改为成功
        this.status = FULFILLED;
        //保存成功之后的值
        this.value = value;
        //判断成功回调是否存在 如果存在 调用
        //this.successCallback && this.successCallback(this.value);
        while (this.successCallback && this.successCallback.length) {
            this.successCallback.shift()();
        }
    };
    reject = (reason) => {
        if (this.status !== PENDING) return;
        //将状态更改为失败
        this.status = REJECTED;
        //保存失败的原因
        this.reason = reason;
        //判断失败回调是否存在  如果存在  调用
        //this.failCallback && this.failCallback(this.reason);
        while (this.failCallback && this.failCallback.length)
            this.failCallback.shift()();
    };
    then(successCallback, failCallback) {
        successCallback = successCallback ? successCallback : value => value
        failCallback = failCallback ? failCallback : reason => {
            throw reason
        }
        let promise2 = new MyPromise((resolve, reject) => {
            //判断状态
            if (this.status === FULFILLED) {
                setTimeout(() => {
                    try {
                        let x = successCallback(this.value);
                        //判断x 的值是普通值还是promise对象
                        //如果是普通值 直接调用resolve
                        //如果是promise对象 查看promise对象返回的结果
                        //再根据promise对象返回的结果 决定调用resolve还是调用reject
                        resolvePromise(promise2, x, resolve, reject);
                        // resolve(x);
                    } catch (e) {
                        reject(e)
                    }
                }, 0);
            } else if (this.status === REJECTED) {
                setTimeout(() => {
                    try {
                        let x = failCallback(this.reason);
                        //判断x 的值是普通值还是promise对象
                        //如果是普通值 直接调用resolve
                        //如果是promise对象 查看promise对象返回的结果
                        //再根据promise对象返回的结果 决定调用resolve还是调用reject
                        resolvePromise(promise2, x, resolve, reject);
                        // resolve(x);
                    } catch (e) {
                        reject(e)
                    }
                }, 0);
            } else {
                //等待
                //将成功 和失败回调存储起来
                this.successCallback.push(() => {
                    setTimeout(() => {
                        try {
                            let x = successCallback(this.value);
                            //判断x 的值是普通值还是promise对象
                            //如果是普通值 直接调用resolve
                            //如果是promise对象 查看promise对象返回的结果
                            //再根据promise对象返回的结果 决定调用resolve还是调用reject
                            resolvePromise(promise2, x, resolve, reject);
                            // resolve(x);
                        } catch (e) {
                            reject(e)
                        }
                    }, 0);
                });
                this.failCallback.push(() => {
                    setTimeout(() => {
                        try {
                            let x = failCallback(this.reason);
                            //判断x 的值是普通值还是promise对象
                            //如果是普通值 直接调用resolve
                            //如果是promise对象 查看promise对象返回的结果
                            //再根据promise对象返回的结果 决定调用resolve还是调用reject
                            resolvePromise(promise2, x, resolve, reject);
                            // resolve(x);
                        } catch (e) {
                            reject(e)
                        }
                    }, 0);
                });
            }
        });

        return promise2;
    }
    finally(callback) {
        return this.then(value => {
            return MyPromise.resolve(callback()).then(() => value)

        }, reason => {
            callback()
            return MyPromise.resolve(callback()).then(() => {
                throw reason
            })
        })
    } catch (failCallback) {
        return this.then(undefined, failCallback)
    }
    static all(array) {
        let result = []
        let index = 0
        return new MyPromise((resolve, reject) => {
            function addData(key, value) {
                result[key] = value
                index++
                if (index === array.length) {
                    resolve(result)
                }
            }
            for (let i = 0; i < array.length; i++) {
                let current = array[i]
                if (current instanceof MyPromise) {
                    //promise对象
                    current.then(value => addData(i, value), (reason) => {
                        reject(reason)
                    })
                } else {
                    //普通值
                    addData(i, array[i])
                }
            }
        })
    }
    static resolve(value) {
        if (value instanceof MyPromise) return value
        return new MyPromise(resolve => {
            resolve(value)
        })
    }
}

function resolvePromise(promise2, x, resolve, reject) {
    if (promise2 === x) {
        return reject(
            new TypeError("Chaining cycle detected for promise #<Promise>")
        );
    }
    if (x instanceof MyPromise) {
        //promise对象
        // x.then(
        //     (value) => {
        //         resolve(value);
        //     },
        //     (reason) => {
        //         reject(reason);
        //     }
        // );
        x.then(resolve, reject);
    } else {
        resolve(x);
    }
}

module.exports = MyPromise;